Types of Studio and Live Microphones

Microphones are needed any time natural audio must be captured by electronic equipment. In a sense, they are the opposite of speakers. A speaker converts analog electrical signals into sound waves by moving the speaker’s cone. A microphone converts sound waves to electrical signals via a diaphragm.

There are a number of different types of microphones on the market, each of which has been created to provide certain capabilities and capture certain types of sounds. The best type to use in any particular application depends upon the sound that is being produced, the volume of that sound, the frequency range of that sound and the location of the microphone in relation to that sound. All of these factors need to be taken into account when selecting the best possible microphone to use.

There is some difference in recording in a studio situation as opposed to providing sound amplification in a live situation. In a live situation, the sound engineer or technician has less ability to control the sound that is coming into the microphone. This requires better control of the microphone, so that it only picks up what is wanted. At the same time, live situations tend to be harder on equipment, so the microphones used need to be more robust and less susceptible to damage.

Basic Microphone Types

There are three basic types of microphones, defined by how they convert sound to electricity. While they are all intended to do this basic function, they do it slightly differently. This creates a difference in how they respond to the sound, specifically their frequency response.

All microphones need amplification before their signal is usable. Sound systems are typically designed to allow for more than adequate amplification, under the assumption that it is best to not have equipment operating at maximum power. This also provides more flexibility for the user, as they can use a variety of different types of microphones together, adjusting the gain on each to meet its output.

Dynamic Microphones

Dynamic Microphones are the most common type. Basically, if the microphone looks like an ice cream cone with the ice cream covered by a window screen, it’s probably a dynamic microphone. These are common because they are relatively inexpensive to manufacture, extremely rugged, and provide a reasonable frequency response. However, they need a fairly loud sound to capture and they are not very good at extremely high frequency sounds.

A dynamic microphone consists of a thin plastic membrane which is connected to a very small coil of copper wire that is suspended in a magnetic field. As sound vibrations strike the diaphragm, they cause it to move, creating an analog electrical signal.

The problem with dynamic microphones is that all of the power is produced by the coil. This creates a couple of problems. First of all, the output signal is extremely weak, requiring amplification to be useful. Unfortunately, the more a signal is amplified, the more possibility there is for the introduction of noise in the signal. The second problem is that the diaphragm and coil have some mass (albeit very little) which resists movement. That makes it very hard for dynamic microphones to capture high frequency sounds accurately.

Condenser or Capacitor Microphones

The difference between a capacitor microphone and a dynamic microphone is that the capacitor microphone has an “air” capacitor instead of a coil. This capacitor consists of two metal plates, one connected to the diaphragm and the other fixed. Typically, instead of attaching a metal plate to the diaphragm, the diaphragm is gold plated, allowing it to act as one of the plates. Vibration of the diaphragm causes the space between these plates to vary. If a fixed electrical charge is applied to the capacitor, then it will become modulated by the change in capacitance.

Capacitor microphones need to receive this power, commonly referred to as “phantom power” to be supplied by the sound mixer board they are attached to. These microphones are much more efficient than dynamic microphones and can handle frequencies that are higher than the limit of human hearing with great accuracy. Larger diaphragm microphones are typically used for voice, providing a warmer, flatter sound. Small diaphragm models are used when high accuracy is required.

Capacitor microphones can only be used with balanced lines, due to the need of the signal lines to carry the 48 volt power for the microphone to operate on. While they are more sensitive than dynamic microphones, they are also considerably more expensive.

Electret Microphones

Electret microphones are a variation on the capacitor microphone, where the diaphragm is permanently charged. This eliminates the need for phantom power, but also makes the diaphragm much heavier. Instead of having the higher frequency response found on most capacitor microphones, they have a frequency response similar to that of dynamic microphones. Some electret microphones are referred to as “electret condenser” recognizing that they are a sub-category of condenser microphones.

There is a type of electret microphone, called the “back electret,” which charges the back plate of the capacitor, rather than the diaphragm. This allows for the same lighter diaphragm that is used in a capacitor microphone, and the associated frequency response. However, the phantom power is not needed.

Some electrets microphones use an internal battery to power the capacitor, thereby eliminating the need for phantom power. As a general rule of thumb, these microphones produce a higher volume level, almost as if they were amplified.

Microphone Pickup Patterns

In addition to the type of microphone construction, one must take into consideration the pickup pattern the microphone offers. The pickup patter is the area around the microphone where sound waves can come from, and the microphone will be able to pick them up. This is an important factor in microphone selection, as often there are things which should not be picked up (such as monitor speakers).

omnidirectional polar pattern

Omnidirectional – The omnidirectional microphone is designed for use in situations where there is no concern about the microphone picking up sound from the back side of the microphones, specifically sound from monitor speakers. This type of pickup pattern is very common for tie clip microphones.

 

Cardoid polar pattern

Cardioid – The cardiod pattern is so named because it is heart shaped. The pickup patter covers about a 120 degree arc to the front of the microphone. This is the most common type of microphone for live performances, as it effectively blocks out the sound from the floor monitors and the audience.

 

hypercardiod polar pattern

Supercardioid or Hypercardioid – The supercardioid provides a tighter pattern than the cardioid, picking up about a 120 degree arc of sound to the front. However, in doing this, it can also pick up some sound to the back, although it has less sensitivity to that direction. Supercardioid microphones are useful when several singers are working together, so that their individual voices can be isolated. The monitor needs to be places a bit to the side, to prevent feedback.

shotgun polar pattern

Shotgun or Zoom – Shotgun microphones are commonly used in the motion picture industry and for video cameras. They effectively cut out almost all sound, except a narrow angle of sound (about 60 degrees) to the front. This prevents problems with picking up anything other than the actors. It also helps eliminate the “tunnel effect” so common when using microphones to pick up someone who is several feet from the camera.

figure 8 polar pattern

Bidirectional or Figure 8 – These microphones pick up equally to the front and rear of the microphone. As such, they are excellent for picking up a conversation between two people. They are commonly used in radio control booths and in studios.

 

Please note that for these diagrams, the microphone is pointing towards the top of the page.

Wireless vs. Wired Microphones

In the last 30 years, wireless microphones have gained a lot of popularity for live performances. They provide the performer with a greater freedom of movement, eliminating the need to be concerned about dragging a “tail” around with them. However, wireless microphones are more susceptible to electrical interference, especially from other types of radios operating nearby. For this reason, they are not used in studio applications.

 

Rich Murphy